Fc-independent functions of anti-CTLA-4 antibodies contribute to anti-tumor efficacy.

Ipilimumab, a monoclonal antibody that recognizes cytotoxic T-lymphocyte associated protein 4 (CTLA-4), was the first immune checkpoint inhibitor approved by the FDA to treat metastatic melanoma patients. Multiple preclinical studies have proposed that Fc effector functions of anti-CTLA-4 therapy are required for anti-tumor efficacy, in part, through the depletion of intratumoral regulatory T cells (Tregs). However, the contribution of the Fc-independent functions of anti-CTLA-4 antibodies to the observed efficacy is not fully understood. H11, a non-Fc-containing single-domain antibody (VHH) against CTLA-4, has previously been demonstrated to block CTLA-4-ligand interaction. However, in vivo studies demonstrated lack of anti-tumor efficacy with H11 treatment. Here, we show that a half-life extended H11 (H11-HLE), despite the lack of Fc effector functions, induced potent anti-tumor efficacy in mouse syngeneic tumor models. In addition, a non-Fc receptor binding version of ipilimumab (Ipi-LALAPG) also demonstrated anti-tumor activity in the absence of Treg depletion. Thus, we demonstrate that Fc-independent functions of anti-CTLA-4 antibodies contributed to anti-tumor efficacy, which may indicate that non-Treg depleting activity of anti-CTLA-4 therapy could benefit cancer patients in the clinic.

Ubiquitin-activating enzyme inhibition induces an unfolded protein response and overcomes drug resistance in myeloma.

Three proteasome inhibitors have garnered regulatory approvals in various multiple myeloma settings; but drug resistance is an emerging challenge, prompting interest in blocking upstream components of the ubiquitin-proteasome pathway. One such attractive target is the E1 ubiquitin-activating enzyme (UAE); we therefore evaluated the activity of TAK-243, a novel and specific UAE inhibitor. TAK-243 potently suppressed myeloma cell line growth, induced apoptosis, and activated caspases while decreasing the abundance of ubiquitin-protein conjugates. This was accompanied by stabilization of many short-lived proteins, including p53, myeloid cell leukemia 1 (MCL-1), and c-MYC, and activation of the activating transcription factor 6 (ATF-6), inositol-requiring enzyme 1 (IRE-1), and protein kinase RNA-like endoplasmic reticulum (ER) kinase (PERK) arms of the ER stress response pathway, as well as oxidative stress. UAE inhibition showed comparable activity against otherwise isogenic cell lines with wild-type (WT) or deleted p53 despite induction of TP53 signaling in WT cells. Notably, TAK-243 overcame resistance to conventional drugs and novel agents in cell-line models, including bortezomib and carfilzomib resistance, and showed activity against primary cells from relapsed/refractory myeloma patients. In addition, TAK-243 showed strong synergy with a number of antimyeloma agents, including doxorubicin, melphalan, and panobinostat as measured by low combination indices. Finally, TAK-243 was active against a number of in vivo myeloma models in association with activation of ER stress. Taken together, the data support the conclusion that UAE inhibition could be an attractive strategy to move forward to the clinic for patients with relapsed and/or refractory multiple myeloma.